1. Field of the Invention
This invention relates to an electric capacitor using a polyvinylidene fluoride film as a dielectric.
2. Description of the Prior Art
Of late communication devices, such as radios, televisions and tape recorders, have gradually been miniaturized using transistors, integrated circuits, and the like. Accordingly, it is necessary that the electrical component parts used in these devices be miniaturized also. With organic film capacitors, many efforts in miniaturization have been made to satisfy this requirement, such as simplifying the armor, thinning the dielectric film, or developing a film having a high dielectric constant.
However, the miniaturization of an electric capacitor by simplifying its armor is necessarily limited due to the necessity of retaining the heat resistance and humidity resistance characteristics. As a result miniaturization is difficult.
Previous attempts to thin a polyester film to 4 microns and a polycarbonate film to 2 microns have generally been unsatisfactory because the defects in the film itself are increased and making a capacitor is very difficult by such thinning. A film having a high dielectric constant is a polyvinyl fluoride film and a polyvinylidene fluoride film. These films are generally thinned by the use of solvents and have a dielectric constant of about 6 to 8, that is, about 2 to 3 times as much as the dielectric constant of known organic films for capacitors. For example, a polyethylene film has a dielectric constant of 2.2; polypropylene film 2.1; polystyrene film 2.6; polyester film 3.2; and polycarbonate film 3.0. These films are not practical to use as a dielectric, because the electrical characteristics of the capacitor utilizing them are inferior. Such capacitors have a dielectric loss of 2 to 3%, a volume resistivity of 1 to 3 .times. 10.sup.14 .OMEGA.-cm, a dielectric breakdown strength of 90 to 120 kilovolts/mm. (KV/mm) and electrically defective points such as conductive fine particles and 20 or more pinholes per square centimeter. The dimensional stability is poor, having a heat shrinkage ratio of 6% or larger at 100.degree. C. or 15% or larger at 150.degree. C., resulting in the dielectric film being shrunk and deformed by the high temperatures used during capacitor making and resulting in an incomplete connection with an outgoing terminal.